Mass storage requirements for computers have matured substantially since the introduction of the personal computer. In the current computing environment, whether for large systems or personal computers, typical requirements for mass storage devices are in the hundreds of megabytes to several gigabytes. In conjunction with such mass storage requirements are the data security issues which require that these large mass storage devices be backed up in one way or another to ensure that there is minimal loss of data even in the event of a system failure.
There are several ways to achieve these goals. A conventional approach for the mass storage device is one or more fixed disk drives permanently mounted within a chassis. A typical approach for data backup is a tape drive providing archival storage. In some high end systems, such as file servers, it is known to provide mirrored drives, in which a two functionally identical drives are installed with one drive serving as the backup to the other drive. In many such systems, a tape backup is also provided to provide archival storage.
There are a number of difficulties with these approaches to mass storage and backup devices. One difficulty with permanently installed drives is that, in the event of a failure, the entire system must be taken down to replace the drive; even if the system includes mirrored drives, it is generally not recommended to disconnect a permanently installed drive while the system is powered up. Part of the problem relates to the fact that the drives are installed within the cabinet, and are not readily accessible without substantial disassembly of the system.
A second difficulty involves the availability of multiple drive bays for a system. In a conventional system, the number of drive bays available for mass storage devices can be fairly limited. While oversized cabinets have been built to accommodate the desire for multiple, large drives, the trend toward smaller, more compact systems is at odds with the desire for large storage capacities.
A third difficulty with permanently installed drives is that the capacity is limited to a specific number of megabytes. Even if a large capacity is initially provided, a truism in the industry is that capacity will eventually be reached.
A fourth difficulty relates to problems with conventional archival storage devices. Tape backups generally provide inexpensive but slow data storage, where data retrieval times are measured in minutes rather than milliseconds. While this delay is not necessarily bad in every instance, it is certainly undesirable in many applications. In addition, the accuracy of tape as a media is frequently in question.
Finally, a fifth difficulty relates to portability of the data. Permanently installed drives offer little portability, and a failure of another component in the system using exclusively permanently installed drives renders the entire system useless and the data inaccessible. While tape drives offer some solution to this problem, the effort in reinstalling a significant amount of software from tape onto a machine not the source of that data frequently makes the process so slow and inefficient as to be unworkable.
Removable media drives are known in the industry, and offer some limited success in overcoming a few of the foregoing limitations of conventional prior art systems. For example, SyQuest Technology offers cartridge drives in which the media can be removed from the remainder of the drive. While this approach does offer the ability to expand the capacity of a drive, the media in a SyQuest cartridge is readily exposed to the environment and can easily become contaminated from such exposure, rendering the cartridge useless. In addition, Bernoulli drives offer removable media, but suffer from slow access time and limited reliability. In addition, none of these devices can be readily hot swapped, and each of them has, historically, taken up at least a half-height drive bay for a single device. Importantly, the limited storage capacity of these devices makes them unsatisfactory as a primary drive or, in at least a number of cases, a backup device.
The assignee of the present invention has, in the past, offered a solution to some, but not all, of the foregoing limitations of the prior art. The aforementioned U.S. patent application Ser. No. 07/764,590, filed Sep. 24, 1991, discloses a removable disk drive of sufficient capacity to be installed as either a primary drive, a secondary drive, or a backup device. Moreover, the unit offers relatively fast access times, unlimited expansion of total capacity through the use of multiple cartridges, and shirt pocket portability. However, the device disclosed there did not include means for hot swapping of drives; that is, exchanging drives while the system is still operating without loss of data, and also provides only a single cartridge per half-height bay. In addition, while the docking module provided there operates well for many users, a method for simply ensuring that the drive is fully installed or disconnected is desirable.
As a result, there has been a need for a removable cartridge drive which improves upon the foregoing limitations of the prior art.